Application Ser. No. 07/356,375
Application Ser. No. 07/356,375 relates to commutation control methods and circuitry for switched reluctance electric motors.
In a plural phase switched reluctance electric motor, the phases are energized in cyclic sequence, generally one phase at a time, though some overlap may be desirable in certain applications. The cyclic sequence of energization of the phases creates a rotating magnetic field producing a torque on the rotor which then rotates to follow the rotating magnetic field. Generally, when the rotor reaches a maximum alignment position relative to the presently energized phase, the next phase should then be energized, to maximize torque production. The change from one motor state energizing one phase to the next motor state energizing the next phase is called commutation. It is desirable to know the position of the rotor, in order to select the proper commutation timing and phase energization, and hence provide the optimum magnetic field pattern for producing optimum torque on the rotor.
Various commutation methods are known in the prior art for commutating to the next motor state to energize the next phase. Various external sensors are known for sensing rotor position. A drawback of external sensors is that they add cost to the motor control, and require additional wiring.
Various sensorless motor control systems are known in the prior art. These systems sense a given motor parameter, such as inductance as measured by back EMF, a frequency change in switching because of an inductance change, a test pulse current in an non-energized winding, and so on. A drawback of these methods is that they are motor-dependent, i.e. inductance varies from motor to motor and with differing sizes, manufacturers, and construction methods. Another drawback is that such methods only provide a general reference point for where the motor is in its rotation.
Application Ser. No. 07/356,375 provides a control method which is motor-independent, and which senses an actual change in motor operation, not just a change in a motor parameter. Application Ser. No. 07/356,375 further enables an exact position reference for the motor. In application Ser. No. 07/356,375, regeneration current is sensed in the energized phase of a switched reluctance electric motor. In the preferred embodiment, individual phase regeneration current is sensed. In an alternate embodiment, bus regeneration current is sensed.